Low pressure mercury arc discharge lamps are standard lighting means which include electrodes sealed in a glass envelope, the interior of which may be coated with a phosphor. The lamp also contains a small amount of mercury and an inert gas at low pressure, of about 1 to 5 torr. The term lamp, as used herein, means the complete unit including the glass envelope and the end pieces and plugs for mounting in a lamp fixture, and wires which connect the internal components of the envelope with the end pieces.
In manufacture of fluorescent or low pressure mercury arc lamps an amount of elemental mercury (Hg.sup.0) is sealed in the lamp envelope. Most of the mercury adheres to the phosphor coating, a small amount being in the vapor phase.
During operation, alkali metal carbonates from the electrodes decompose and form free oxygen in the lamp. The oxygen may react with a portion of the mercury to form soluble mercury oxide (HgO). Soluble mercury oxide is leachable from land fills and other disposal facilities. Soluble mercury oxides or other oxidized forms of mercury are detrimental to the accuracy and reliability of the standard test for determination of the leachability of toxic materials from lamp waste. This test is generally referred to as the Toxicity Leaching Characteristic Procedure or TLCP test.
There is concern about the environmental impact of soluble mercury compounds which can leach into ground water sources, rivers, streams, and the like.
Elimination of soluble, i.e., leachable, mercury is a desirable result in the TCLP test and for the environment when lamps are disposed of in a landfill.
The formation of leachable mercury when fluorescent lamps are broken and exposed to landfill conditions can be prevented or minimized by preventing oxidation of metal components of the lamp. Certain metal components of fluorescent lamps particularly iron lead wires and any brass components generate ferric (Fe.sup.+3) ions when exposed to moisture, oxygen, and acidity.
In order to address the growing concern that excessive amounts of mercury from disposal of fluorescent lamps might leach into surface and subsurface bodies of water, the Environmental Protection Agency has established a maximum concentration level for mercury at 200 parts per billion. This is generally determined by the standard analysis known as the Toxicity Characteristic Leaching Procedure (TCLP), a well known test procedure.
In carrying of the TCLP test, the lamps are pulverized to form lamp waste material similar to that which would result from lamp disposal in land fills or other disposal locations. The ambient conditions in such locations may be such as to promote formation of leachable mercury just as the TCLP test conditions themselves tend to allow for formation of leachable mercury in amounts greater than the established limit of 0.2 milligrams per liter.
It has been found that elemental mercury added to mercury-free pulverized lamp materials prepared for the TCLP test is converted to leachable mercury in the course of the test. If elemental mercury alone or in combination with various glass, phosphor, and other non-metal lamp components is tested, little or essentially no leachable mercury is found. When elemental mercury is tested in combination with metal lamp components such as iron lead wires, pins, or other metal hardware, the mercury has been found to be transformed into a leachable form.
It was determined by controlled experimentation that ferric iron (trivalent) is generated under the TCLP test conditions when carried out in the presence of oxygen and that this ionic species is able to oxidize elemental mercury to soluble mercury compounds which are measured as leachable mercury.
Corrosion or dissolution of metals from the metallic state requires the presence of both oxygen and a solvent such as water conditions that exist in the TCLP test and landfill situations. Accordingly, it has been found that the formation can be controlled or prevented by controlling or excluding exposure to oxygen of the iron containing metal lamp components.
The principles and practice of this invention will be more fully understood when considered in view of the following examples.
All TCLP test data was obtained by the test procedure prescribed on pages 26987-26998 volume 55, number 126 of the June 29, 1990 issue of the Federal Register.
Briefly, lamps being tested are pulverized into particulate form having the prescribed particle size which is capable of passing through 3/8 inch sieve. The test material is then extracted with a sodium acetate-acetic acid buffer at a pH of about 4.93.
To prevent the formation of leachable mercury upon disposal of mercury vapor discharge lamps and to improve the reliability of the TCLP test the formation of soluble iron is controlled by use of iron-free or low iron parts as components for lamp manufacture.
The effect of both soluble iron and copper on the formation of soluble mercury is evident from the data in Table 1, below. As the head space volume(available oxygen) increases, the amount of soluble mercury increases in response to the formation of increasing amounts of soluble iron (ferric) and copper.
TABLE 1 Head Space Soluble Soluble Soluble (mL) Mercury (ppb) Iron (ppm) Copper (ppm) 0 0.0000 210 3.62 0.35 1 140 214 4.63 0.40 2 205 203 5.04 0.63
Table 2, below, shows the effect of iron content on the formation of leachable mercury in the TCLP test procedure described above.
TABLE 2 Fe mg Leachable Hg ppm Soluble Fe ppm 0.2000 50.000 0.50000 1.1000 108.00 0.50000 10.100 158.00 3.2000 103.30 165.00 27.600
The object of the invention is to disclose a method to introduce soluble copper reagents that are capable of reducing upon the metal components of lamps in the TCLP test. The reduced forms of the copper salts that plate upon aluminum or other metal surfaces inhibit the generation of oxidized forms of mercury within the TCLP test.